The invention relates to a gravity flow storage system for storing loaded pallets. More particularly, it relates to a "LIFO" (last-in/first-out) storage system intended for use in confined areas wherein lift truck access is only available at one end of the system.
In conventional drive-in or aisle-type fixed rack storage systems, lift trucks are required for every product or pallet movement. In contrast, a gravity flow or live storage system makes use of conveyors fitted with wheels or rollers, and suitable speed control devices, which are selected according to the type of pallet used in the system. The conveyors are inclined at a slight angle with respect to the floor. After a pallet is initially loaded into the system, it moves at a controlled speed under the force of gravity towards the lower end or discharge face of the rack system where it can be removed by fork lift, stacker, or other material handling equipment. This type of gravity flow storage system is frequently referred to as a "first in/first out" ("FIFO") storage system.
These gravity flow systems can provide high storage density due to the elimination of access aisles previously needed to allow lift trucks to maneuver while loading and unloading pallets. In addition, the storage system operating requirements for fork lift truck operations, loading times, and operating personnel can be substantially reduced. Moreover, with such gravity flow storage systems, high storage density is also achieved because no empty space is left between the stored pallets, which abut each other under the force of gravity. In such storage systems, it is only necessary to access the loading face where the pallets are placed into the storage system, and the discharge face from where the pallets are removed. In between the loading and discharge faces, pallets move "downstream" automatically by gravity, without the assistance of any other operator-controlled material handling equipment.
Such "FIFO" gravity flow storage systems have been quite successful for relatively large storage facilities. However, they typically are not suitable in small storage facilities where because of dimensional and configurational restrictions it is not possible to provide adequate access space for the loading and discharge ends of the rack system. For example, the storage area may be long and narrow with access available at only one narrow end. Moreover, even if sufficient access were available at both narrow ends of such a storage space, it might be more advantageous for applications where a variety of different products are being stored to have access to a large number of pallet storage lanes having a relatively short multi-pallet depth (e.g., 3-5 pallets) rather than just two or three long lanes.
To accommodate such smaller storage facilities, a variety of "LIFO" (Last-in/First-out) gravity flow storage systems have been proposed wherein, the rollers or conveyors are inclined from the rear end of the rack, which is normally situated against a wall. The front end of the conveyor provides access for both loading and unloading pallets onto the rack. However, these storage systems have been relatively complex and often themselves occupy a substantial amount of space, thereby significantly reducing the available storage space in any particular application.
Specifically, one known system utilizes ovelying or stacked carts having wheels which roll upon inclined rails However, the overlying nature of the carts causes them to occupy additional height and width within the storage system, thereby wasting storage space. In addition, because they must carry the entire pallet weight directly, the overlying carts must be constructed from relatively large and heavy structural members, and include a centrally located support or cross beam. This not only takes up additional storage space, but it also requires the system structure be sufficient to carry not only the payload weight of the pallets, but also the substantial weight of the carts themselves. Moreover, the crossbeams of the carts tend to interfere with the insertion of lifting forks during fork-lift operations. In addition, each cart requires its own set of wheels.
Another important consideration in rack storage is that the bottom surface of a conventional wooden pallet is generally poorly suited for acting as a roller facing or bearing surface. While it is possible that such pallets can be moved directly on wheel or roller conveyor in a flow storage system, their operation therein is erratic and pallets frequently "hang-up" in the upstream position. In such cases, operating personnel may be required to climb into the supporting structure to free "stuck" pallets, thereby subjecting themselves to possible injury. Similarly, broken or defective wooden pallets cannot be conveyed safely and reliably in conventional flow storage racks. Moreover, existing storage systems cannot easily handle "slave" pallets which are generally made of plywood or steel, and are usually from 3/4" to 11/2" thick but without provision for lift truck forks to enter into the pallet itself. Hence, the forks support the pallet on its bottom surface, and in such cases, existing systems using carts are not practical, because setting the pallet down on the cart is impossible, due to the position of the forks in between the cart and pallet.
Accordingly, it is an object of the present invention to provide a flow storage system that may be operated with access to only one of its ends.
It is also an object of the invention to provide such a flow storage system having an automatic last in/first out ("LIFO") rotation of inventory.
Yet another object of the present invention is to provide such a flow storage system capable of readily operating with slave pallets and with conventional wooden pallets, even if they are broken or defective.
It is yet another object of the present invention to provide such a flow storage system which itself is compact and thereby allows for a maximum amount of storage space therein.
It is yet another object of the invention to provide such a flow storage system which may be easily loaded and unloaded by a fork-lift truck.
It is still another object of the invention to provide such a flow storage system which is of simple and economical construction, easy to use and install, and which is safe and reliable in operation.